In known transmissions of this type (shown in German Patent Specification No. 18 06 501 laid open July 3, 1969, German Patent Specification No. 25 35 700 laid open Feb. 10, 1977), it has been attempted, through the use of as many identical elements as possible, for instance, gears having the same number of gear teeth, and also by modular assembling of the shifting units, to reduce the cost of manufacture of such gears and be able to vary the number of gear ratios.